The purpose of this study is to clarify the process of the transition from prelinguistic vocalizations to two-word speech.
Three children were observed from about seven months to the beginning of two-word speech every three weeks. The vocalizations which they uttered for twenty minutes in the manipulation of objects and play were analysed.
The spontaneous vocalizations were divided into babbling, protolanguage and language. Through the percentage of each vocalization, the outlines of the transition were clarified. In protolanguage, phonetically consistent forms were observed in a particular context. Four function categories for the phonetically consistent forms - affect expressions, instrumental expressions, indicating expressions and grouping expressions which Dore et al (1976) reported, - were identified.
First words emerged at 9 or 10 months and the referential words increased after the demonstratives, ie, here, this, appeared. Before two-word speech began, the word combinations which were accompanied by an interjection and a particle, and repetition of words ernerged. At about 18-20 months, two-word speech began.
The vocalizations, except the babbling, had meanings which were categorized into eight functions : personal, interpersonal, instrumental, descriptive, regulatory, question, informative and imaginative functions. The order above represents the sequence of the emergence. After the emergence of the instrumental vocalizations, the first words appeared. The appearance of the regulatory vocalizations correspond to the emergence of the referential words.
Vocal imitations were not only sound repetitions, but had the meanings mentioned before. After the demonstratives emerged, vocal imitations with descriptive functions increased and contributed to the acqisition of words.
From these results about language development of normal children, some suggestions were able to evolve for the training of language-delayed children.